Journal of Neuroscience, Vol 13, 632-649, Copyright © 1993 by Society for Neuroscience
Confocal microscopy reveals coordinated calcium fluctuations and oscillations in synaptic boutons
N Melamed, PJ Helm and R Rahamimoff
Department of Physiology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Calcium ions are one of the main factors regulating quantal transmitter
release and thus synaptic transmission in the nervous system. Using
confocal microscopy, fluorescent imaging with the calcium indicator Rhod-2,
and time series analysis, we show that the levels of calcium ions inside
single synaptic boutons of the lizard neuromuscular junction are not
constant at rest, but undergo coordinated fluctuations in the space domain,
which cover a large fraction of the synaptic bouton. Furthermore,
oscillations in intracellular calcium were frequently observed in the time
domain. Control experiments showed no coordinated fluctuations or
oscillations at locations outside the synaptic boutons. Edge detection
analysis showed that the coordinated fluctuations and oscillations were not
due to movement artifacts. No coordinated fluctuations and oscillations
were seen when similar measurements and analyses were performed on
artificial fluorescent beads. A variance analysis was performed on
artificial fluorescent beads and on synaptic boutons. The variance of the
fluorescent signal at the synaptic boutons was larger than the variance in
artificial beads with the same mean fluorescence. This extra variance was
greatly reduced when the extracellular calcium concentration was decreased
from 2.0 mM to 0.4 mM. We conclude that the coordinated fluctuations and
oscillations in the calcium-induced fluorescence at the synaptic boutons
are genuine biological phenomena and may be of significance in the
regulation of transmitter release.
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